The retina is uniquely situated for optical access, densely populated with mitochondria, and markedly responsive to oxygen supply. These features are combined in our proposal to monitor the dynamics of oxidative energy metabolism in animal and human retinas in vivo. We use a dual wavelength spectrophotometer adapted to a fundus camera to direct monochromatic light onto the ocular fundus and detect the light that has transilluminated the retina and is reflected our again. Spectral absorption peaks for respiratory chain cytochromes are selected for optical monitoring and the intensity of reflected light at that wavelength, referenced to a nearby wavelength, provides an immediate, on-line readout of oxygen utilization and supply in the retina. Vascular volume changes are measured concurrently. Our experimental protocol includes analysis of the kinetics of oxygenation of normal and ischemic retinas to step-changes in inspired oxygen, using an ischemic model in experimental animals at present, and in the future patients with ocular vascular insufficiency, particularly diabetic retinopathy. Also planned are data on the correlation between the electroretinogram and the reduction-oxydation level of the cytochromes in response to oxygen tensions ranging from acute hypoxia to hyperbaric oxygen combined with hypercapnia. In summary, this research effort has as its goal the establishment of relationships between mitochondrial redox states and oxygen demand in the living retina, and an appraisal of those physiological factors affecting retinal blood flow, vascular tone, and oxygen transport.